Evolution of the gene model and its relationship to wild-type and mutant phenotypes. Over the past century, the definition of a gene has been improved and refined from its conceptual origin in the early 1900’s (A) with the discovery of RNA and DNA structures (B), splicing (C), and lastly, widespread unannotated transcription (D). Exonic regions are depicted as blue boxes with transcripts shown as arrows below (spliced and unspliced). A hypothetical mutation is shown as a red triangle. Note that as the definition of a gene grows to include multiple transcripts, a single mutation can now affect many different transcripts and thus potentially could have multiple and more subtle phenotypes.
